प्रकृतेः क्रियमाणानि गुणैः कर्माणि सर्वशः। अहङ्कारविमूढात्मा कर्ताऽहमिति मन्यते ॥

prakṛiteḥ kriyamāṇāni guṇaiḥ karmāṇi sarvaśhaḥ ahankāra-vimūḍhātmā kartāham iti manyate

All actions are wrought by the quali ties of nature only. The self, deluded by egoism, thinketh: "I am the doer."

In plain words: Krishna says all actions are really carried out by the forces of nature, which he calls the qualities. But a person fooled by ego thinks, "I am the one doing it."